1) Field of the Invention
The present invention relates to electrodes and, in particular, to an elongate electrode that is integrated with a structural member and provides a path of electrical conductivity, for example, for transmitting signals or power through the structural member.
2) Description of Related Art
Electrical devices are often used in conjunction with a structural member. For example, electrical devices such as sensors and actuators can be embedded within, mounted on, or otherwise structurally integrated with the structure of a vehicle such as an airplane, spacecraft, land vehicle, ship, and the like. Other examples of electrical devices mounted in conjunction with a structural member can include machinery, buildings, and the like. The sensors can be used to detect temperature, motion, stress, strain, damage, and the like at different locations throughout the structure. The actuators can be used to adjust various control portions of the structure such as an elevator, rudder, aileron, helicopter rotor, door, or valve. Data generated by the electrical devices is typically communicated via electrical wires from the devices to a computer or other circuit device for processing. Similarly, control signals and electrical power are typically transmitted via electrical wires from the computer, power supply, and/or other circuit device to the actuators and sensors. Thus, a network of wires is often required for controlling and monitoring the electrical devices. Each wire usually includes one or more conductive strands, for example, copper strands, which are covered with an insulative jacket. Parallel wires can be held in groups with bundle fasteners, such as cable tie straps or shrink tubing. Fasteners such as clips, ties, and the like are often used to connect the wires or bundles of wires to the structural member at successive locations along the length of the wires so that the position of the wires is maintained.
In some applications, however, it is difficult or impractical to connect the wires to the structural member. For example, the structural member may not define any interior cavities through which the wires can be passed, and the environmental conditions outside the structural member may be harsh, for example, excessively warm or cold or subject to mechanical stress, moisture, or corrosive agents. Further, in applications where the structural member undergoes significant or repeated mechanical stress, the resulting strains in the wires can break the wires regardless of whether the wires are connected to the structural member.
One illustrative example is a blade of a helicopter rotor, which is rotated quickly around a hub of the rotor. In some cases, it may be desirable to provide wires that extend along the length of the blade, for example, to monitor sensors or control actuators in or on the blade. The wires cannot be connected to the outside of the blade because of the external conditions, e.g., wind, moisture, and the like. Further, the blade undergoes significant stress due to centripetal force when rotated at high speeds. If the wires are not connected successively or continuously along the length of the blade, each wire will also be strained due to the centripetal force that results from the rotation. On the other hand, if the wires are connected to the blade, the wires will be strained at the same rate as the blade. In either case, the stress that results in the wires can break or fatigue the wires, rendering the electrical devices ineffective.
Thus, there exists a need for an electrode device that can be provided in a structural member for transmitting electrical signals or power. The electrode should be capable of being integrated with structural members and functioning in harsh environmental conditions that include strain and temperature variations, moisture, and corrosive agents. The electrode should also be adaptable and formable to structural members without internal passages for wiring. Further, the electrode should resist failure, even when the structural member is subjected to significant or repeated stresses.